Network Working Group G. Van de Velde
Internet-Draft T. Hain
Intended status: Informational R. Droms
Expires: April 16, 2007 Cisco Systems
B. Carpenter
IBM
E. Klein
Tel Aviv University
October 13, 2006
Network Architecture Protection for IPv6<draft-ietf-v6ops-nap-04.txt>
Status of this Memo
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This Internet-Draft will expire on April 16, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
Although there are many perceived benefits to Network Address
Translation (NAT), its primary benefit of "amplifying" available
address space is not needed in IPv6. In addition to NAT's many
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Internet-Draft Network Architecture Protection for IPv6 October 20061. Introduction
There have been periodic claims that IPv6 will require a Network
Address Translation (NAT), because with IPv4 people use NAT to
accomplish that person's preferred task. This document will explain
why those pronouncements are false by showing how to accomplish the
task goal without address translation. Although there are many
perceived benefits to NAT, its primary benefit of "amplifying"
available address space is not needed in IPv6. The serious
disadvantages and impact on applications by ambiguous address space
and Network Address Translation [1] [5]have been well documented [4]
[6]so there will not be much additional discussion here. However,
given its wide deployment NAT undoubtedly has some perceived
benefits, though the bulk of those using it have not evaluated the
technical trade-offs. Indeed, it is often claimed that some
connectivity and security concerns can only be solved by using a NAT
device, without any mention of the negative impacts on applications.
This is amplified through the widespread sharing of vendor best
practice documents and sample configurations that do not
differentiate the translation function of address expansion from the
state function of limiting connectivity.
This document describes the goals for utilizing a NAT device in an
IPv4 environment that are regularly cited as solutions for perceived
problems. It then shows how these needs can be met without using the
header modification feature of NAT in an IPv6 network. It should be
noted that this document is 'informational', as it discusses
approaches that will work to accomplish the goals. It is
specifically not a BCP that is recommending any one approach.
As far as security and privacy are concerned, this document considers
how to mitigate a number of threats. Some are obviously external,
such as having a hacker or a worm infected machine outside trying to
penetrate and attack the local network. Some are local such as a
disgruntled employee disrupting business operations, or the
unintentional negligence of a user downloading some malware which
then proceeds to attack from within. Some may be inherent in the
device hardware ("embedded") such as having some firmware in a
domestic appliance "call home" to its manufacturer without the user's
consent.
Another consideration discussed is the view that NAT can be used to
fulfill the goals of a security policy. At a technical level the
translation process fundamentally can not produce security because
mangling the address in the header does not fulfill any useful
security functions; in fact it breaks the ability to produce an audit
trail which is a fundamental security tool. That said, the artifacts
of NAT devices do provide some value.
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1. The need to establish state before anything gets through from
outside to inside solves one set of problems.
2. The need to stop receiving any packets when finished with a flow
solves a set of problems
3. the need to appear to be attached at the edge of the network
solves a set of problems
4. and the ability to have addresses that are not publicly routed
solves yet another set (mostly changes where the state is and
scale requirements for the first one).
This document describes several techniques that may be combined in an
IPv6 deployment to protect the integrity of its network architecture.
It will focus on the 'how to accomplish a goal' perspective, leaving
most of the 'why that goal' perspective for other documents. These
techniques, known collectively as Network Architecture Protection
(NAP6), retain the concept of a well defined boundary between
"inside" and "outside" the private network, and allow firewalling,
topology hiding, and privacy. NAP6 will achieve these security goals
without address translation whilst regaining the ability for
arbitrary any-to-any connectivity.
IPv6 Network Architecture Protection can be summarized in the
following table. It presents the marketed "benefits" of IPv4+NAT
with a cross-reference of how those are delivered in both the IPv4
and IPv6 environments.
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concludes with a IPv6 NAP6 case study and a gap analysis of work that
remains to be done for a complete NAP6 solution.
2. Perceived Benefits of NAT and its Impact on IPv4
This section provides insight into the generally perceived benefits
of the use of IPv4 NAT. The goal of this description is not to
analyze these benefits or the accuracy of the perception (detailed
discussions in [4]), but to describe the deployment requirements and
set a context for the later descriptions of the IPv6 approaches for
dealing with those requirements.
2.1. Simple Gateway between Internet and Private Network
A NAT device can connect a private network with addresses allocated
from any part of the space (ambiguous [1] or global registered &
unregistered address) towards the Internet, though extra effort is
needed when the same range exists on both sides of the NAT. The
address space of the private network can be built from globally
unique addresses, from ambiguous address space or from both
simultaneously. In the simple case of private use addresses, without
needing specific configuration the NAT device enables access between
the client side of a distributed client-server application in the
private network and the server side located in the public Internet.
Wide-scale deployments have shown that using NAT to act as a simple
gateway attaching a private IPv4 network to the Internet is simple
and practical for the non-technical end user. Frequently a simple
user interface, or even a default configuration is sufficient for
configuring both device and application access rights.
This simplicity comes at a price as the resulting topology puts
restrictions on applications. The NAT simplicity works well when the
applications are limited to a client/server model with the server
deployed on the public side of the NAT. For peer-to-peer, multi-
party, or servers deployed on the private side of the NAT, helper
technologies must be available. These helper technologies are
frequently complex to develop and manage, creating a hidden cost to
this 'simple gateway'.
2.2. Simple Security due to Stateful Filter Implementation
It is frequently believed that through its session-oriented
operation, NAT puts in an extra barrier to keep the private network
protected from outside influences. Since a NAT device typically
keeps state only for individual sessions, attackers, worms, etc.
cannot exploit this state to attack a specific host on any other
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port, though in the port overload case of NAPT attacking all active
ports will impact a potentially wide number of hosts. This benefit
may be partially real, however, experienced hackers are well aware of
NAT devices and are very familiar with private address space, and
have devised methods of attack (such as trojan horses) that readily
penetrate NAT boundaries. For these reasons the sense of security
provided by NAT is actually an illusion.
The act of address translation does not provide security in itself;
for example, consider a configuration with static NAT translation and
all inbound ports translating to a single machine. In such a
scenario the security risk for that machine is identical to the case
with no NAT device in the communication path. As result there is no
specific security value in the address translation function. The
perceived security of NAT comes from the lack of pre- established or
permanent mapping state. Dynamically establishing state in response
to internal requests reduces the threat of unexpected external
connections to internal devices. This role, often marketed as a
firewall, is really an arbitrary artifact while a real firewall has
explicit management controls.
In some cases, NAT operators (including domestic users) may be
obliged to configure quite complex port mapping rules to allow
external access to local applications such as a multi-player game or
web servers. In this case the NAT actually adds management
complexity compared to a simple router. In situations where two or
more devices need to host the same application or otherwise use the
same public port this complexity shifts from difficult to impossible.
2.3. User/Application tracking
One usage of NAT is for the local network administrator to track user
and application traffic. Although NATs create temporary state for
active sessions, in general they provide limited capabilities for the
administrator of the NAT to gather information about who in the
private network is requesting access to which Internet location.
This is done by periodically logging the network address translation
details of the private and the public addresses from the NAT device's
state database.
The subsequent checking of this database is not always a simple task,
especially if Port Address Translation is used. It also has an
unstated assumption that the administrative instance has a mapping
between a private IPv4-address and a network element or user at all
times, or the administrator has a time-correlated list of the
address/port mappings.
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Internet-Draft Network Architecture Protection for IPv6 October 20062.4. Privacy and Topology Hiding
One goal of 'topology hiding' is to prevent external entities from
making a correlation between the topological location of devices on
the local network. The ability of NAT to provide Internet access to
a large community of users by the use of a single (or a few) global
IPv4 routable addresses offers a simple mechanism to hide the
internal topology of a network. In this scenario the large community
will be represented in the Internet by a single (or a few) IPv4
address(es).
The use of NAT then results in a user behind a NAT gateway actually
appearing from the Internet as a user inside the NAT box itself;
i.e., the IPv4 address that appears on the Internet is only
sufficient to identify the NAT so all internal nodes appear to exist
at the demarcation edge. When concealed behind a NAT it is
impossible to tell from the outside which member of a family, which
customer of an Internet cafe, or which employee of a company
generated or received a particular packet. Thus, although NATs do
nothing to provide application level privacy, they do prevent the
external tracking and profiling of individual systems by means of
their IP addresses, usually known as 'device profiling'.
At the same time a NAT creates a smaller pool of addresses for a much
more focused point of attack, where the adversary does not need to
scan the entire local network but can instead concentrate on the
active ports associated with the NAT adress. By periodically
scanning the limited 16 bit port range on the public side of the NAT,
the attack will routinely find all ports that are open to active
nodes.
There is a similarity with privacy based on application level
proxies. When using an application level gateway for browsing the
web for example, the 'privacy' of a web user can be provided by
masking the true identity of the original web user towards the
outside world (although the details of what is - or is not - logged
at the NAT/proxy will be different).
Some network managers prefer to hide as much as possible of their
internal network topology from outsiders as a useful precaution to
mitigate scanning attacks. Mostly this is achieved by blocking
"traceroute" etc., though NAT entirely hides the internal subnet
topology. Scanning is a particular concern in IPv4 networks because
the subnet size is small enough that once the topology is known it is
easy to find all the hosts, then start scanning them for vulnerable
ports. Once a list of available devices has been mapped, a port-scan
on these IP addresses can be performed. Scanning works by tracking
which ports do not receive unreachable errors from either the
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firewall or host. With the list of open ports an attacker can
optimize the time needed for a successful attack by correlating it
with known vulnerabilities to reduce the number of attempts. For
example, FTP usually runs on port 21, and HTTP usually runs on port
80. Any vulnerable open ports could be used for access to an end
system to command it to start initiating attacks on others.
2.5. Independent Control of Addressing in a Private Network
Many private IPv4 networks take benefit from using the address space
defined in RFC 1918 to enlarge the available addressing space for
their private network, and at the same time reduce their need for
globally routable addresses. This type of local control of address
resources allows a sufficiently large pool for a clean and
hierarchical addressing structure in the local network.
Another benefit is due to the usage of independent addresses on
majority of the network infrastructure there is an increased ability
to change provider with less operational difficulties.
Section 2.7 describes some disadvantages that appear if independent
networks using ambiguous addresses [1]have to be merged.
2.6. Global Address Pool Conservation
While the widespread use of IPv4+NAT has reduced the potential
consumption rate, the ongoing depletion of the IPv4 address range has
already taken the remaining pool of unallocated IPv4 addresses below
25%. While mathematical models based on historical IPv4 prefix
consumption periodically attempt to predict the future exhaustion
date of the IPv4 address pool, a direct result of this continuous
resource consumption is that the administrative overhead for
acquiring globally unique IPv4 addresses will continue increasing in
direct response to tightening allocation policies.
In response to the increasing administrative overhead many Internet
Service Providers (ISPs) have already resorted to the ambiguous
addresses defined in RFC 1918 behind a NAT for the various services
they provide as well as connections for their end customers. This
happens even though the private use address-space is strictly limited
in size. Some deployments have already outgrown that space and have
begun cascading NAT to continue expanding, though this practice
eventually breaks down over routing ambiguity. Additionally, while
we are unlikely to know the full extent of the practice (because it
is hidden behind a nat), service providers have been known to
announce previously unallocated public space to their customers (to
avoid the problems associated with the same address space appearing
on both sides), only to find that once that space was formally
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allocated and being publicly announced their customers couldn't reach
the registered networks.
The number of and types of applications that can be deployed by these
ISPs and their customers is restricted by the ability to overload the
port range on the public side of the most public NAT in the path.
The limit of this approach is something substantially less than 2^48
possible active **application** endpoints (approximately [2^32 minus
2^29] * [2* 2^16 minus well known port space]), as distinct from
addressable devices each with their own application endpoint range.
Those who advocate layering of NAT frequently forget to mention that
there are topology restrictions placed on the applications. Forced
into this limiting situation such customers can rightly claim that
despite the optimistic predictions of mathematical models, the global
pool of IPv4 addresses is effectively already exhausted.
2.7. Multihoming and Renumbering with NAT
Allowing a network to be multihomed and renumbering a network are
quite different functions. However these are argued together as
reasons for using NAT, because making a network multihomed is often a
transitional state required as part of network renumbering, and NAT
interacts with both in the same way.
For enterprise networks, it is highly desirable to provide resiliency
and load-balancing to be connected to more than one Internet Service
Provider (ISP) and to be able to change ISPs at will. This means
that a site must be able to operate under more than one CIDR prefix
[16]and/or readily change its CIDR prefix. Unfortunately, IPv4 was
not designed to facilitate either of these maneuvers. However, if a
site is connected to its ISPs via NAT boxes, only those boxes need to
deal with multihoming and renumbering issues.
Similarly, if two enterprise IPv4 networks need to be merged and
RFC1918 addresses are used, there is a high probability of address
overlaps. In those situations it may well be that installing a NAT
box between them will avoid the need to renumber one or both. For
any enterprise, this can be a short term financial saving, and allow
more time to renumber the network components. The long term solution
is a single network without usage of NAT to avoid the ongoing
operational complexity of overlapping addresses.
The addition of an extra NAT as a solution may be sufficient for some
networks; however when the merging networks were already using
address translation it will create major problems due to
administrative difficulties of overlapping address spaces in the
merged networks.
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Internet-Draft Network Architecture Protection for IPv6 October 20063. Description of the IPv6 Tools
This section describes several features that can be used as part of
the NAP6 solution to replace the protection features associated with
IPv4 NAT.
The reader must clearly distinguish between features of IPv6 that
were fully defined when this document was drafted and those that were
potential features that still required more work to define them. The
latter are summarized later in the 'Gap Analysis' section of this
document. However, we do not distinguish in this document between
fully defined features of IPv6 and those that were already widely
implemented at the time of writing.
3.1. Privacy Addresses (RFC 3041)
There are situations where it is desirable to prevent device
profiling, for example by web sites that are accessed from the device
as it moves around the Internet. IPv6 privacy addresses were defined
to provide that capability. IPv6 addresses consist of a routing
prefix, subnet-id part (SID) and an interface identifier part (IID).
As originally defined, IPv6 stateless address auto-configuration
(SLAAC) will typically embed the IEEE Link Identifier of the
interface as the IID part, though this practice facilitates tracking
and profiling of a device through the consistent IID. RFC 3041 [7]
describes an extension to SLAAC to enhance device privacy. Use of
the privacy address extension causes nodes to generate global-scope
addresses from interface identifiers that change over time,
consistent with system administrator policy. Changing the interface
identifier (thus the global-scope addresses generated from it) over
time makes it more difficult for eavesdroppers and other information
collectors to identify when addresses used in different transactions
actually correspond to the same node. A relatively short valid
lifetime for the privacy address also has the side effect of reducing
the attack profile of a device, as it is not directly attackable once
it stops answering at the temporary use address.
While the primary implementation and source of randomized RFC 3041
addresses is expected to be from end-systems running stateless auto-
configuration, there is nothing that prevents a DHCP server from
running the RFC 3041 algorithm for any new IEEE identifier it hears
in a request, then remembering that for future queries. This would
allow using them in DNS for registered services since the assumption
of a DHCP server based deployment would be a persistent value that
minimizes DNS churn. A DHCP based deployment would also allow for
local policy to periodically change the entire collection of end
device addresses while maintaining some degree of central knowledge
and control over which addresses should be in use at any point in
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time.
Randomizing the IID, as defined in RFC 3041, is effectively a sparse
allocation technique which only precludes tracking of the lower 64
bits of the IPv6 address. Masking of the subnet ID will require
additional approaches as discussed below in 3.4. Additional
considerations are discussed in [19].
3.2. Unique Local Addresses
Achieving the goal of autonomy, that many perceive as a value of NAT,
is required for local network and application services stability
during periods of intermittent connectivity or moving between one or
more providers. Such autonomy in a single routing prefix environment
would lead to massive expansion of the global routing tables (as seen
in IPv4), so IPv6 provides for simultaneous use of multiple prefixes.
The Unique Local Address prefix (ULA) [15]has been set aside for use
in local communications. The ULA address prefix for any network is
routable over a locally defined collection of routers. These
prefixes are not intended to be routed on the public global Internet
as large scale inter-domain distribution of routes for ULA prefixes
would have a negative impact on global route aggregation.
ULAs have the following characteristics:
o For all practical purposes a globally unique prefix
* Allows networks to be combined or privately interconnected
without creating address conflicts or requiring renumbering of
interfaces using these prefixes
* If accidentally leaked outside of a network via routing or DNS,
it is highly unlikely that there will be a conflict with any
other addresses
o ISP independent and can be used for communications inside of a
network without having any permanent or only intermittent Internet
connectivity
o Well-known prefix to allow for easy filtering at network
boundaries preventing leakage of local routes and packets.
o In practice, applications may treat these addresses like global
scoped addresses but address selection algorithms may need to
distinguish between ULAs and ordinary global scope unicast
addresses to assure stability. The policy table defined in [10]
is one way to bias this selection, by giving higher preference to
FC00::/7 over 2001::/3. Mixing the two kinds of addresses may
lead to undeliverable packets during times of instability, but
that mixing is not likely to happen when the rules of RFC 3484 are
followed.
o ULAs have no intrinsic security properties. However, they have
the useful property that their routing scope is limited by default
within an administrative boundary. Their usage is suggested at
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several points in this document, as a matter of administrative
convenience.
3.3. DHCPv6 Prefix Delegation
One of the functions of a simple gateway is managing the local use
address range. The Prefix Delegation (DHCP-PD) options [11] provide
a mechanism for automated delegation of IPv6 prefixes using the
Dynamic Host Configuration Protocol (DHCP) [9]. This mechanism
(DHCP-PD) is intended for delegating a long-lived prefix from a
delegating router (possibly incorporating a DHCPv6 server) to a
requesting router, possibly across an administrative boundary, where
the delegating router does not require knowledge about the topology
of the links in the network to which the prefixes will be assigned.
3.4. Untraceable IPv6 Addresses
The main goal of untraceable IPv6 addresses is to create an
apparently amorphous network infrastructure as seen from external
networks to protect the local infrastructure from malicious outside
influences and from mapping of any correlation between the network
activities of multiple devices from external networks. When using
untraceable IPv6 addresses, it could be that two apparently
sequential addresses are allocated to devices on very different parts
of the local network instead of belonging to devices adjacent to each
other on the same subnet.
Since IPv6 addresses will not be in short supply even within a single
/64 (or shorter) prefix, it is possible to generate them effectively
at random when untraceability is required. They will be globally
routable IPv6 addresses under the site's prefix, which can be
randomly and independently assigned to IPv6 devices. The random
assignment is intended to mislead the outside world about the
structure of the local network. In particular the subnet structure
may be invisible in the address. Thus a flat routing mechanism will
be needed within the site. The local routers need to maintain a
correlation between the topological location of the device and the
untraceable IPv6 address. For smaller deployments this correlation
could be done by generating IPv6 host route entries, or for larger
ones by utilizing an indirection device such as a Mobile IPv6 Home
Agent. Additional details are in section 4.7.
4. Using IPv6 Technology to Provide the Market Perceived Benefits of NAT
The facilities in IPv6 described in Section 3 can be used to provide
the protection perceived to be associated with IPv4 NAT. This
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section gives some examples of how IPv6 can be used securely.
4.1. Simple Gateway between Internet and Internal Network
As a simple gateway, the device manages both packet routing and local
address management. A basic IPv6 router should have a default
configuration to advertise inside the site a locally generated random
ULA prefix, independently from the state of any external
connectivity. This would allow local nodes in a topology more
complex than a single link to communicate amongst themselves
independent of the state of a global connection. If the network
happened to concatenate with another local network, the randomness in
ULA creation is highly unlikely to result in address collisions.
With external connectivity the simple gateway should use DHCP-PD to
acquire a routing prefix from the service provider for use when
connecting to the global Internet. End-system connections involving
other nodes on the global Internet will always use the global IPv6
addresses derived from this prefix delegation. It should be noted
that the address selection policy table in end-systems defined in RFC3484 should be configured to prefer the ULA prefix range over the
DHCP-PD prefix range when the goal is to keep local communications
stable during periods of transient external connectivity.
In the very simple case there is no explicit routing protocol on
either side of the gateway, and a single default route is used
internally pointing out to the global Internet. A slightly more
complex case might involve local internal routing protocols, but with
the entire local network sharing a common global prefix there would
still not be a need for an external routing protocol as the service
provider could install a route for the prefix delegated via DHCP-PD
pointing toward the connecting link.
4.2. IPv6 and Simple Security
The vulnerability of an IPv6 host is similar to that of an IPv4 host
directly connected towards the Internet. The use of firewall and
Intrusion Detection Systems (IDS) is recommended for those that want
boundary protection in addition to host defenses. A proxy may be
used for certain applications, but with the caveat that the end to
end transparency is broken. However, with IPv6, the following
protections are available without the use of NAT while maintaining
end-to-end reachability:
1. Short lifetimes on privacy extension suffixes reduce the attack
profile since the node will not respond to the address once its
lifetime becomes invalid.
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2. IPsec is a mandatory service for IPv6 implementations. IPsec
functions to authenticate the correspondent, prevent session
hijacking, prevent content tampering, and optionally masks the
packet contents. While IPsec is commonly available in some IPv4
implementations and can support NATs, NAT support has limitations
and does not work in all situations. In addition, the use of
IPsec with NATs consumes extra bandwidth for UDP encapsulation
and keepalive overhead [12]. In the IPv4/NAT environment, the
usage of IPSec has been largely limited to edge-to-edge VPN
deployments, its potential for end-to-end deployment is
significantly enhanced in an IPv6 network. It should be noted
that encrypted IPsec traffic will bypass content-aware firewalls,
which is presumed to be acceptable for parties with whom the site
has established a security association.
3. The size of the address space of a typical subnet (64 bits of
IID) will make a complete subnet ping sweep virtually impossible
due to the potential number of combinations available. Reducing
the security threat of port scans on identified nodes requires
sparse distribution within the subnet to minimize the probability
of scans finding adjacent nodes. This scanning protection will
be nullified if IIDs are configured in any structured groupings
within the IID space. Provided that IIDs are essentially
randomly distributed across the available space, address scanning
based attacks will effectively fail. This protection exists if
the attacker has no direct access to the specific subnet and
therefore is trying to scan it remotely. If an attacker has
local access then he could use ND [3]and ping6 to the link-scope
multicast ff02::1 to detect the IEEE based address of local
neighbors, then apply the global prefix to those to simplify its
search (of course, a locally connected attacker has many scanning
options with IPv4 as well).
Assuming the network administrator is aware of [20]the increased size
of the IPv6 address will make topology probing much harder, and
almost impossible for IPv6 devices. The intention of topology
probing is to identify a selection of the available hosts inside an
enterprise. This mostly starts with a ping-sweep. Since the IPv6
subnets are 64 bits worth of address space, this means that an
attacker has to send out a simply unrealistic number of pings to map
the network, and virus/worm propagation will be thwarted in the
process. At full-rate full-duplex 40Gbps (400 times the typical
100Mbps LAN, and 13,000 times the typical DSL/Cable access link) it
takes over 5000 years to scan the entirety of a single 64 bit subnet.
IPv4 NAT was not developed as a security mechanism. Despite
marketing messages to the contrary it is not a security mechanism,
and hence it will offer some security holes while many people assume
their network is secure due to the usage of NAT. IPv6 security best
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practices will avoid this kind of illusory security but can only
address the same threats if correctly configured firewalls and IDS
systems are used at the perimeter.
It must be noted that even a firewall doesn't fully secure
a network. Many attacks come from inside or are at a layer
higher than the firewall can protect against. In the final
analysis, every system has to be responsible for its own
security, and every process running on a system has to be
robust in the face of challenges like stack overflows etc.
What a firewall does is prevent a network administration
from having to pay for bandwidth to carry unauthorized
traffic, and in so doing reduce the probability of certain
kinds of attacks across the protected boundary.
To implement simple security for IPv6 in, for example, a DSL
connected home network, the DSL broadband gateway/router should be
equipped with stateful firewall capabilities. These should provide a
default configuration where incoming traffic is limited to return
traffic resulting from outgoing packets (sometimes known as
reflective session state). There should also be an easy interface
which allows users to create inbound 'pinholes' for specific purposes
such as online-gaming. Another consideration would be the capability
for service provider mediated pinhole management where things like
voice call signaling could dynamically establish pinholes based on
predefined authentication rules.
Administrators and the designers of configuration interfaces for
simple IPv6 firewalls need to provide a means of documenting the
security caveats that arise from a given set configuration rules so
that users (who are normally oblivious to such things) can be made
aware of the risks. As rules are improved iteratively, the goal will
be to make use of the IPv6 Internet more secure without increasing
the perceived complexity for users who just want to accomplish a
task.
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Internet-Draft Network Architecture Protection for IPv6 October 20064.3. User/Application Tracking
IPv6 enables the collection of information about data flows. Due to
the fact that all addresses used for Internet and intra-/inter- site
communication are unique, it is possible for an enterprise or ISP to
get very detailed information on any communication exchange between
two or more devices. Unless privacy addresses [7] are in use, this
enhances the capability of data- flow tracking for security audits
compared with IPv4 NAT, because in IPv6 a flow between a sender and
receiver will always be uniquely identified due to the unique IPv6
source and destination addresses.
At the same time, this tracking is per address. In environments
where the goal is tracking back to the user, additional external
information will be necessary correlating a user with an address. In
the case of short lifetime privacy address usage, this external
information will need to be based on more stable information such as
the layer 2 media address.
4.4. Privacy and Topology Hiding using IPv6
Partial host privacy is achieved in IPv6 using pseudo-random privacy
addresses RFC 3041 which are generated as required, so that a session
can use an address that is valid only for a limited time. This only
allows such a session to be traced back to the subnet that originates
it, but not immediately to the actual host, where IPv4 NAT is only
traceable to the most public NAT interface.
Due to the large IPv6 address space available there is plenty of
freedom to randomize subnet allocations. By doing this, it is
possible to reduce the correlation between a subnet and its location.
When doing both subnet and IID randomization [7]a casual snooper
won't be able to deduce much about the networks topology. The
obtaining of a single address will tell the snooper very little about
other addresses. This is different from IPv4 where address space
limitations cause this to be not true. In most usage cases this
concept should be sufficient for address privacy and topology hiding,
with the cost being a more complex internal routing configuration.
As discussed in Section 3.1, there are multiple parts to the IPv6
address, and different techniques to manage privacy for each which
may be combined to protect the entire address. In the case where a
network administrator wishes to fully isolate the internal IPv6
topology, and the majority of its internal use addresses, one option
is to run all internal traffic using Unique Local Addresses (ULA).
By definition this prefix block is not to be advertised into the
public routing system, so without a routing path external traffic
will never reach the site. For the set of hosts that do in fact need
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to interact externally, by using multiple IPv6 prefixes (ULAs and one
or more global addresses) all of the internal nodes that do not need
external connectivity, and the internally used addresses of those
that do will be masked from the outside. The policy table defined in
[10]provides a mechanism to bias the selection process when multiple
prefixes are in use such that the ULA would be preferred when the
correspondent is also local.
There are other scenarios for the extreme situation when a network
manager also wishes to fully conceal the internal IPv6 topology. In
these cases the goal in replacing the IPv4 NAT approach is to make
all of the topology hidden nodes appear from the outside to logically
exist at the edge of the network, just as they would when behind a
NAT.
o One approach uses explicit host routes in the IGP to remove the
external correlation between physical topology attachment point
and end-to-end IPv6 address. In the figure below the hosts would
be allocated prefixes from one or more logical subnets, and would
inject host routes to internally identify their real attachment
point. This solution does however show severe scalability issues
and requires hosts to securely participate in the IGP, as well as
having the firewall block all external to internal traceroute for
the logical subnet. The specific limitations are dependent on the
IGP protocol, the physical topology, and the stability of the
system. In any case the approach should be limited to uses with
substantially fewer than the maximum number of routes that the IGP
can support (generally between 5,000 and 50,000 total entries
including subnet routes). Hosts should also listen to the IGP for
duplicate use before finalizing an interface address assignment as
the duplicate address detection will only check for use on the
attached segment, not the logical subnet.
o Another technical approach to fully hide the internal topology is
use of a tunneling mechanism. Mobile IPv6 without route
optimization is one approach for using an automated tunnel, as it
always starts in tunnel mode via the Home Agent (HA). In this
deployment model the application perceived addresses of the nodes
are routed via the edge HA. This indirection method truly masks
the internal topology, as from outside the local network all nodes
with global access appear to share the prefix of one or more
logical subnets attached to the HA rather than their real
attachment point. Duplicate address detection is handled as a
normal process of the HA binding update. While turning off all
binding updates with the coorespondent node would appear to be
necessary to prevent leakage of topology information, that
approach would also force all internal traffic using the home
address to route via the HA tunnel, which may be undesirable. A
more efficient method would be to allow internal route
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optimizations while dropping outbound binding update messages at
the firewall. Another approach for the internal traffic would be
to use the policy table of RFC 3484 to bias a ULA prefix as
preferred internally, leaving the logical subnet Home Address
external for use. The downsides with a Mobile IPv6 based solution
is that it requires a home agent in the network, the configuration
of a security association with the HA for each hidden node, and
consumes some amount of bandwidth for tunnel overhead.
o Another method (where the layer 2 topology allows) uses a virtual
lan approach to logically attach the devices to one or more
subnets on the edge router. This approach leads the end nodes to
believe they actually share a common segment. The downsides of
this approach is that all internal traffic would be directed over
sub-optimal paths via the edge router, as well as the complexity
of managing a distributed logical lan.
Internet
|
\
|
+------------------+
| topology |-+-+-+-+-+-+-+-+--
| masking | Logical subnets
| router |-+-+-+-+-+-+-+-+--
+------------------+ for topology
| hidden nodes
|
Real internal -------------+-
topology | |
| -+----------
-----------+--------+
|
|
|
One issue to be aware of is that subnet scope multicast will not work
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for the logical hidden subnets, except in the vlan case. While a
limited scope multicast to a collection of nodes that are arbitrarily
scattered makes no technical sense, care should be exercised to avoid
deploying applications that expect limited scope multicast in
conjunction with topology hiding.
Another issue that this document will not define is the mechanism for
a topology hidden node to learn its logical subnet. While manual
configuration would clearly be sufficient, DHCP could be used for
address assignment, with the recipient node discovering it is in a
hidden mode when the attached subnet prefix doesn't match the one
assigned.
4.5. Independent Control of Addressing in a Private Network
IPv6 provides for autonomy in local use addresses through ULAs. At
the same time IPv6 simplifies simultaneous use of multiple addresses
per interface so that an IPv6 NAT is not required between the ULA and
the public Internet because nodes that need access to the public
Internet will have a global use address as well. When using IPv6,
the need to ask for more address space will become far less likely
due to the increased size of the subnets, along with an allocation
policy that recognizes table fragmentation is also an important
consideration. While global IPv6 allocation policy is managed
through the Regional Internet Registries, it is expected that they
will continue with derivatives of [8] for the foreseeable future so
the number of subnet prefixes available to an organization should not
be a limitation which would create an artificial demand for NAT.
Ongoing subnet address maintenance may become simpler when IPv6
technology is utilized. Under IPv4 address space policy restrictions
each subnet must be optimized, so one has to look periodically into
the number of hosts on a segment and the subnet size allocated to the
segment and rebalance. For example an enterprise today may have a
mix of IPv4 /28 - /23 size subnets, and may shrink/grow these as
their network user base changes. For IPv6 all subnets have /64
prefixes which will reduce the operational and configuration
overhead.
4.6. Global Address Pool Conservation
IPv6 provides sufficient space to completely avoid the need for
overlapping address space. Since allocations in IPv6 are based on
subnets rather than hosts a reasonable way to look at the pool is
that there are about 17*10^18 unique subnet values where sparse
allocation practice within those provides for new opportunities such
as SEND 3971 [13]. As previously discussed, the serious
disadvantages of ambiguous address space have been well documented,
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and with sufficient space there is no need to continue the
increasingly aggressive conservation practices that are necessary
with IPv4. While IPv6 allocation policies and ISP business practice
will continue to evolve, the recommendations in RFC 3177 are based on
the technical potential of the vast IPv6 address space. That
document demonstrates that there is no resource limitation which will
require the adoption of the IPv4 workaround of ambiguous space behind
a NAT. As an example of the direct contrast, many expansion oriented
IPv6 deployment scenarios result in multiple IPv6 addresses per
device, as opposed to the constriction of IPv4 scenarios where
multiple devices are forced to share a scarce global address through
a NAT.
4.7. Multihoming and Renumbering
IPv6 was designed to allow sites and hosts to run with several
simultaneous CIDR allocated prefixes, and thus with several
simultaneous ISPs. An address selection mechanism [10] is specified
so that hosts will behave consistently when several addresses are
simultaneously valid. The fundamental difficulty that IPv4 has in
regard to multiple addresses therefore does not apply to IPv6. IPv6
sites can and do run today with multiple ISPs active, and the
processes for adding, removing, and renumbering active prefixes at a
site have been documented in [14] and [21]. However, multihoming and
renumbering remain technically challenging even with IPv6 with
regards to, for instance, session continuity across multihoming
events or interactions with ingress filtering (but see the Gap
Analysis below).
The IPv6 address space allocated by the ISP will be dependent upon
the connecting Service provider. This will likely result in a
renumbering effort when the network changes between service
providers. When changing ISPs or ISPs readjusting their addressing
pool, DHCP-PD [11] can be used as an almost zero- touch external
mechanism for prefix change in conjunction with a ULA prefix for
internal connection stability. With appropriate management of the
lifetime values and overlap of the external prefixes, a smooth make-
before-break transition is possible as existing communications will
continue on the old prefix as long as it remains valid, while any new
communications will use the new prefix.
5. Case Studies
In presenting these case studies we have chosen to consider
categories of network divided first according to their function
either as carrier/ISP networks or end user (such as enterprise)
networks with the latter category broken down according to the number
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of connected end hosts. For each category of networks we can use
IPv6 Network Architecture Protection to achieve a secure and flexible
infrastructure, which provides an enhanced network functionality in
comparison with the usage of address translation.
o Medium/Large Private Networks (typically >10 connections)
o Small Private Networks (typically 1 to 10 connections)
o Single User Connection (typically 1 connection)
o ISP/Carrier Customer Networks
5.1. Medium/large private networks
The majority of private enterprise, academic, research, or government
networks fall into this category. Many of these networks have one or
more exit points to the Internet. Though these organizations have
sufficient resources to acquire addressing independence when using
IPv4 there are several reasons why they might choose to use NAT in
such a network. For the ISP there is no need to import the IPv4
address range from the remote end-customer, which facilitates IPv4
route summarization. The customer can use a larger IPv4 address
range (probably with less-administrative overhead) by the use of RFC1918 and NAT. The customer also reduces the overhead in changing to
a new ISP, because the addresses assigned to devices behind the NAT
do not need to be changed when the customer is assigned a different
address by a new ISP. By using address translation in IPv4 one
avoids the expensive process of network renumbering. Finally, the
customer can provide privacy for its hosts and the topology of its
internal network if the internal addresses are mapped through NAT.
It is expected that there will be enough IPv6 addresses available for
all networks and appliances for the foreseeable future. The basic
IPv6 address range an ISP allocates for a private network is large
enough (currently /48) for most of the medium and large enterprises,
while for the very large private enterprise networks address-ranges
can be concatenated. The goal of this assignment mechanism is to
decrease the total amount of entries in the public Internet routing
table. A single /48 allocation provides an enterprise network with
65536 different /64 subnet prefixes.
To mask the identity of a user on a network of this type, the usage
of IPv6 privacy extensions may be advised. This technique is useful
when an external element wants to track and collect all information
sent and received by a certain host with known IPv6 address. Privacy
extensions add a random time-limited factor to the host part of an
IPv6 address and will make it very hard for an external element to
keep correlating the IPv6 address to a specific host on the inside
network. The usage of IPv6 privacy extensions does not mask the
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internal network structure of an enterprise network.
When there is need to mask the internal structure towards the
external IPv6 Internet, then some form of 'untraceable' addresses may
be used. These addresses will appear to exist at the external edge
of the network, and may be assigned to those hosts for which topology
masking is required or which want to reach the IPv6 Internet or other
external networks. The technology to assign these addresses to the
hosts could be based on DHCPv6 or static configuration. To
complement the 'Untraceable' addresses it is needed to have at least
awareness of the IPv6 address location when routing an IPv6 packet
through the internal network. This could be achieved by 'host based
route- injection' in the local network infrastructure. This route-
injection could be done based on /128 host-routes to each device that
wants to connect to the Internet using an untraceable address. This
will provide the most dynamic masking, but will have a scalability
limitation, as an IGP is typically not designed to carry many
thousands of IPv6 prefixes. A large enterprise may have thousands of
hosts willing to connect to the Internet.
An alternative for larger deployments is to leverage the tunneling
aspect of MIPv6 even for non-mobile devices. With the logical subnet
being allocated as attached to the edge Home Agent, the real
attachment and internal topology are masked from the outside.
Dropping outbound binding updates at the firewall is also necessary
to avoid leaking the attachment information.
Less flexible masking could be to have time-based IPv6 prefixes per
link or subnet. This may reduce the amount of route entries in the
IGP by a significant factor, but has as trade-off that masking is
time and subnet based which will complicate auditing systems. The
dynamic allocation of 'Untraceable' addresses can also limit the IPv6
access between local and external hosts to those local hosts being
authorized for this capability.
The use of permanent ULA addresses on a site provides the benefit
that even if an enterprise would change its ISP, the renumbering will
only affect those devices that have a wish to connect beyond the
site. Internal servers and services would not change their allocated
IPv6 ULA address, and the service would remain available even during
global address renumbering.
5.2. Small Private Networks
Also known as SOHO (Small Office/Home Office) networks, this category
describes those networks which have few routers in the topology, and
usually have a single network egress point. Typically these networks
are:
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o connected via either a dial-up connection or broadband access
o don't have dedicated Network Operation Center (NOC)
o and through economic pressure are typically forced today to use
NAT
In most cases the received global IPv4 prefix is not fixed over time
and is too long (very often just a /32 just giving a single address)
to provide every node in the private network with a unique globally
usable address. Fixing either of those issues typically adds an
administrative overhead for address management to the user. This
category may even be limited to receiving ambiguous IPv4 addresses
from the service provider based on RFC 1918. An ISP will typically
pass along the higher administration cost attached to larger address
blocks, or IPv4 prefixes that are static over time, due to the larger
public address pool each of those requires.
As a direct response to explicit charges per public address most of
this category has deployed NAPT (port demultiplexing NAT) to minimize
the number of addresses in use. Unfortunately this also limits the
Internet capability of the equipment to being mainly a receiver of
Internet data (client), and makes it quite hard for the equipment to
become a world wide Internet server (i.e. HTTP, FTP, etc.) due to
the stateful operation of the NAT equipment. Even when there is
sufficient technical knowledge to manage the NAT to enable external
access to a server, only one server can be mapped per protocol/
port-number per address, and then only when the address from the ISP
is publicly routed. When there is an upstream NAT providing private
address space to the ISP side of the private NAT, additional
negotiation with the ISP will be necessary to provide an inbound
mapping, if that is even possible.
When deploying IPv6 NAP6 in this environment, there are two
approaches possible with respect to IPv6 addressing.
o DHCPv6 Prefix-Delegation
o ISP provides a static IPv6 address-range
For the DHCPv6-PD solution, a dynamic address allocation approach is
chosen. By means of the enhanced DHCPv6 protocol it is possible to
have the ISP push down an IPv6 prefix range automatically towards the
small private network and populate all interfaces in that small
private network dynamically. This reduces the burden for
administrative overhead because everything happens automatically.
For the static configuration the mechanisms used could be the same as
for the medium/large enterprises. Typically the need for masking the
topology will not be of high priority for these users, and the usage
of IPv6 privacy extensions could be sufficient.
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For both alternatives the ISP has the unrestricted capability for
summarization of its RIR allocated IPv6 prefix, while the small
private network administrator has all flexibility in using the
received IPv6 prefix to its advantage because it will be of
sufficient size to allow all the local nodes to have a public address
and full range of ports available whenever necessary.
While a full prefix is expected to be the primary deployment model
there may be cases where the ISP provides a single IPv6 address for
use on a single piece of equipment (PC, PDA, etc.). This is expected
to be rare though, because in the IPv6 world the assumption is that
there is an unrestricted availability of a large amount of globally
routable and unique address space. If scarcity was the motivation
with IPv4 to provide RFC 1918 addresses, in this environment the ISP
will not be motivated to allocate private addresses towards the
single user connection because there are enough global addresses
available at essentially the same cost. Also it will be likely that
the single device wants to mask its identity to the called party or
its attack profile over a shorter time window than the life of the
ISP attachment, so it will need to enable IPv6 privacy extensions
which in turn leads to the need for a minimum allocation of a /64
prefix rather than a single address.
5.3. Single User Connection
This group identifies the users which are connected via a single IPv4
address and use a single piece of equipment (PC, PDA, etc.). This
user may get an ambiguous IPv4 address (frequently imposed by the
ISP) from the service provider which is based on RFC 1918. If
ambiguous addressing is utilized, the service provider will execute
NAT on the allocated IPv4 address for global Internet connectivity.
This also limits the Internet capability of the equipment to being
mainly a receiver of Internet data, and makes it quite hard for the
equipment to become a world wide Internet server (i.e. HTTP, FTP,
etc.) due to the stateful operation of the NAT equipment.
When using IPv6 NAP6, this group will identify the users which are
connected via a single IPv6 address and use a single piece of
equipment (PC, PDA, etc.).
In IPv6 world the assumption is that there is unrestricted
availability of a large amount of globally routable and unique IPv6
addresses. The ISP will not be motivated to allocate private
addresses towards the single user connection because he has enough
global addresses available, if scarcity was the motivation with IPv4
to provide RFC 1918 addresses. If the single user wants to mask his
identity, he may choose to enable IPv6 privacy extensions.
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Internet-Draft Network Architecture Protection for IPv6 October 20065.4. ISP/Carrier Customer Networks
This group refers to the actual service providers that are providing
the IP access and transport services. They tend to have three
separate IP domains that they support:
o For the first they fall into the Medium/large private networks
category (above) for their own internal networks, LANs etc.
o The second is the Operations network which addresses their
backbone and access switches, and other hardware, this is separate
for both engineering reasons as well as simplicity in managing the
security of the backbone.
o The third is the IP addresses (single or blocks) that they assign
to customers. These can be registered addresses (usually given to
category 5.1 and 5.2 and sometimes 5.3) or can be from a pool of
RFC 1918 addresses used with IPv4 NAT for single user connections.
Therefore they can actually have two different NAT domains that
are not connected (internal LAN and single user customers).
When IPv6 NAP6 is utilized in these three domains then for the first
category it will be possible to use the same solutions as described
in Section 5.1. The second domain of the ISP/carrier is the
Operations network. This environment tends to be a closed
environment, and consequently communication can be done based on ULA
addresses, however, in this environment, stable IPv6 Provider
Independent addresses can be used. This would give a solid and
scalable configuration with respect to a local IPv6 address plan. By
the usage of proper network edge filters, outside access to the
closed environment can be avoided. The third is the IPv6 addresses
that ISP/carrier network assign to customers. These will typically
be assigned with prefix lengths terminating on nibble boundaries to
be consistent with the DNS PTR records. As scarcity of IPv6
addresses is not a concern, it will be possible for the ISP to
provide global routable IPv6 prefixes without a requirement for
address translation. An ISP may for commercial reasons still decide
to restrict the capabilities of the end users by other means like
traffic and/or route filtering etc.
If the carrier network is a mobile provider, then IPv6 is encouraged
in comparison with the combination of IPv4+NAT for 3GPP attached
devices. When looking in chapter 2.3 of RFC3314 'Recommendations for
IPv6 in 3GPP Standards' [17]it is found that the IPv6 WG recommends
that one or more /64 prefixes should be assigned to each primary PDP
context. This will allow sufficient address space for a 3GPP-
attached node to allocate privacy addresses and/or route to a multi-
link subnet, and will discourage the use of NAT within 3GPP-attached
devices.
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Internet-Draft Network Architecture Protection for IPv6 October 20066. IPv6 Gap Analysis
Like IPv4 and any major standards effort, IPv6 standardization work
continues as deployments are ongoing. This section discusses several
topics for which additional standardization, or documentation of best
practice, is required to fully realize the benefits of NAP6. None of
these items are show-stoppers for immediate usage of NAP6 in
scenarios where there are no current gaps.
6.1. Simple Security
Firewall traversal by dynamic pinhole management requires further
study. Several partial solutions exist including ICE [23], UPNP
[24], as well as alternative proposals for Service Provider based
control. The basic security provided by a stateful firewall will
require some degree of default configuration and automation to mask
the technical complexity from a consumer who merely wants a secure
environment with working applications. There is no reason a stateful
IPv6 firewall product cannot be shipped with the equivalent default
protection that is offered by today's IPv4/NAT products.
6.2. Subnet Topology Masking
There really is no functional gap here as a centrally assigned pool
of addresses in combination with host routes in the IGP is an
effective way to mask topology for smaller deployments. If necessary
a best practice document could be developed describing the
interaction between DHCP and various IGPs which would in effect
define Untraceable Addresses.
As an alternative for larger deployments, there is no gap in the HA
tunneling approach when firewalls are configured to block outbound
binding update messages. A border Home Agent using internal
tunneling to the logical mobile node (potentially rack mounted) can
completely mask all internal topology, while avoiding the strain from
a large number of host routes in the IGP. Some optimization work
could be done in Mobile IP to define a policy message where a mobile
node would learn from the Home Agent that it should not try to inform
its correspondent about route optimization and thereby expose its
real location. This optimization which reduces the load on the
firewall would result in less optimal internal traffic routing as
that would also transit the HA. Trade-off's for this optimization
work should be investigated in the IETF.
6.3. Minimal Traceability of Privacy Addresses
Privacy addresses [7] may certainly be used to limit the traceability
of external traffic flows back to specific hosts, but lacking a
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topology masking component above they would still reveal the subnet
address bits. For complete privacy a best practice document
describing the combination of privacy addresses with topology masking
may be required. This work remains to be done, and should be pursued
by the IETF.
6.4. Site Multihoming
This complex problem has never been completely solved for IPv4, which
is exactly why NAT has been used as a partial solution. For IPv6,
after several years of work, the IETF has converged on an
architectural approach intended with service restoration as initial
aim [22]. When this document was drafted, the IETF was actively
defining the details of this approach to the multihoming problem.
The approach appears to be most suitable for small and medium sites,
though it will conflict with existing firewall state procedures. At
this time there are also active discussions in the address registries
investigating the possibility of assigning provider-independent
address space. Their challenge is finding a reasonable metric for
limiting the number of organizations that would qualify for a global
routing entry. Additional work appears to be necessary to satisfy
the entire range of requirements.
7. IANA Considerations
This document requests no action by IANA
8. Security Considerations
While issues which are potentially security related are discussed
throughout the document, the approaches herein do not introduce any
new security concerns. Product marketing departments have widely
sold IPv4 NAT as a security tool and suppliers have been implementing
address translation functionality in their firewalls, though the
misleading nature of those claims has been previously documented in
[2] and [4].
This document defines IPv6 approaches which collectively achieve the
goals of the network manager without the negative impact on
applications or security that are inherent in a NAT approach. To the
degree that these techniques improve a network manager's ability to
explicitly audit or control access, and thereby manage the overall
attack exposure of local resources, they act to improve local network
security.
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Internet-Draft Network Architecture Protection for IPv6 October 20069. Conclusion
This document has described a number of techniques that may be
combined on an IPv6 site to protect the integrity of its network
architecture. These techniques, known collectively as Network
Architecture Protection, retain the concept of a well defined
boundary between "inside" and "outside" the private network, and
allow firewalling, topology hiding, and privacy. However, because
they preserve address transparency where it is needed, they achieve
these goals without the disadvantage of address translation. Thus,
Network Architecture Protection in IPv6 can provide the benefits of
IPv4 Network Address Translation without the corresponding
disadvantages.
The document has also identified a few ongoing IETF work items that
are needed to realize 100% of the benefits of NAP6.
10. Acknowledgements
Christian Huitema has contributed during the initial round table to
discuss the scope and goal of the document, while the European Union
IST 6NET project acted as a catalyst for the work documented in this
note. Editorial comments and contributions have been received from:
Fred Templin, Chao Luo, Pekka Savola, Tim Chown, Jeroen Massar,
Salman Asadullah, Patrick Grossetete, Fred Baker, Jim Bound, Mark
Smith, Alain Durand, John Spence, Christian Huitema, Mark Smith,
Elwyn Davies, Daniel Senie, Soininen Jonne, Lindqvist Erik Kurt and
other members of the v6ops WG.
11. References11.1. Normative References
[1] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E.
Lear, "Address Allocation for Private Internets", BCP 5,
RFC 1918, February 1996.
[2] Srisuresh, P. and M. Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations", RFC 2663, August 1999.
[3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[4] Hain, T., "Architectural Implications of NAT", RFC 2993,
November 2000.
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Internet-Draft Network Architecture Protection for IPv6 October 2006
November 2004.
[19] Dupont, F. and P. Savola, "RFC 3041 Considered Harmful
(draft-dupont-ipv6-rfc3041harmful-05.txt)", June 2004.
[20] Chown, T., "IPv6 Implications for TCP/UDP Port Scanning (chown-
v6ops-port-scanning-implications-01.txt)", July 2004.
[21] Chown, T., Tompson, M., Ford, A., and S. Venaas, "Things to
think about when Renumbering an IPv6 network
(draft-chown-v6ops-renumber-thinkabout-03)", October 2004.
[22] Huston, G., "Architectural Commentary on Site Multi-homing
using a Level 3 Shim (draft-ietf-shim6-arch-00.txt)",
July 2004.
[23] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A
Methodology for Network Address Translator (NAT) Traversal for
Offer/Answer Protocols (draft-ietf-mmusic-ice-11)",
October 2006.
[24] "UPNP Web Site, "Universal Plug and Play Web Site", Web Site
http://www.upnp.org/", July 2005.
Appendix A. Additional Benefits due to Native IPv6 and Universal Unique
Addressing
The users of native IPv6 technology and global unique IPv6 addresses
have the potential to make use of the enhanced IPv6 capabilities, in
addition to the benefits offered by the IPv4 technology.
A.1. Universal Any-to-Any Connectivity
One of the original design points of the Internet was any-to-any
connectivity. The dramatic growth of Internet connected systems
coupled with the limited address space of the IPv4 protocol spawned
address conservation techniques. NAT was introduced as a tool to
reduce demand on the limited IPv4 address pool, but the side effect
of the NAT technology was to remove the any-to-any connectivity
capability. By removing the need for address conservation (and
therefore NAT), IPv6 returns the any-to-any connectivity model and
removes the limitations on application developers. With the freedom
to innovate unconstrained by NAT traversal efforts, developers will
be able to focus on new advanced network services (i.e. peer-to-peer
applications, IPv6 embedded IPsec communication between two
communicating devices, instant messaging, Internet telephony, etc..)
rather than focusing on discovering and traversing the increasingly
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complex NAT environment.
It will also allow application and service developers to rethink the
security model involved with any-to-any connectivity, as the current
edge firewall solution in IPv4 may not be sufficient for any- to-any
service models.
A.2. Auto-configuration
IPv6 offers a scalable approach to minimizing human interaction and
device configuration. Whereas IPv4 implementations require touching
each end system to indicate the use of DHCP vs. a static address and
management of a server with the pool size large enough for the
potential number of connected devices, IPv6 uses an indication from
the router to instruct the end systems to use DHCP or the stateless
auto configuration approach supporting a virtually limitless number
of devices on the subnet. This minimizes the number of systems that
require human interaction as well as improves consistency between all
the systems on a subnet. In the case that there is no router to
provide this indication, an address for use only on the local link
will be derived from the interface media layer address.
A.3. Native Multicast Services
Multicast services in IPv4 were severely restricted by the limited
address space available to use for group assignments and an implicit
locally defined range for group membership. IPv6 multicast corrects
this situation by embedding explicit scope indications as well as
expanding to 4 billion groups per scope. In the source specific
multicast case, this is further expanded to 4 billion groups per
scope per subnet by embedding the 64 bits of subnet identifier into
the multicast address.
IPv6 allows also for innovative usage of the IPv6 address length, and
makes it possible to embed the multicast 'Rendezvous Point' (or RP)
[18] directly in the IPv6 multicast address when using ASM multicast.
This is not possible with limited size of the IPv4 address. This
approach also simplifies the multicast model considerably, making it
easier to understand and deploy.
A.4. Increased Security Protection
The security protection offered by native IPv6 technology is more
advanced than IPv4 technology. There are various transport
mechanisms enhanced to allow a network to operate more securely with
less performance impact:
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o IPv6 has the IPsec technology directly embedded into the IPv6
protocol. This allows for simpler peer-to-peer authentication and
encryption, once a simple key/trust management model is developed,
while the usage of some other less secure mechanisms is avoided
(i.e. md5 password hash for neighbor authentication).
o On a local network, any user will have more security awareness.
This awareness will motivate the usage of simple firewall
applications/devices to be inserted on the border between the
external network and the local (or home network) as there is no
Address Translator and hence no false safety perception.
o All flows on the Internet will be better traceable due to a unique
and globally routable source and destination IPv6 address. This
may facilitate an easier methodology for back-tracing DoS attacks
and avoid illegal access to network resources by simpler traffic
filtering.
o The usage of private address-space in IPv6 is now provided by
Unique Local Addresses, which will avoid conflict situations when
merging networks and securing the internal communication on a
local network infrastructure due to simpler traffic filtering
policy.
o The technology to enable source-routing on a network
infrastructure has been enhanced to allow this feature to
function, without impacting the processing power of intermediate
network devices. The only devices impacted with the source-
routing will be the source and destination node and the
intermediate source-routed nodes. This impact behavior is
different if IPv4 is used, because then all intermediate devices
would have had to look into the source- route header.
A.5. Mobility
Anytime, anywhere, universal access requires MIPv6 services in
support of mobile nodes. While a Home Agent is required for initial
connection establishment in either protocol version, IPv6 mobile
nodes are able to optimize the path between them using the MIPv6
option header while IPv4 mobile nodes are required to triangle route
all packets. In general terms this will minimize the network
resources used and maximize the quality of the communication.
A.6. Merging Networks
When two IPv4 networks want to merge it is not guaranteed that both
networks would be using different address-ranges on some parts of the
network infrastructure due to the usage of RFC 1918 private
addressing. This potential overlap in address space may complicate a
merge of two and more networks dramatically due to the additional
IPv4 renumbering effort. i.e. when the first network has a service
running (NTP, DNS, DHCP, HTTP, etc..) which need to be accessed by
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the 2nd merging network. Similar address conflicts can happen when
two network devices from these merging networks want to communicate.
With the usage of IPv6 the addressing overlap will not exist because
of the existence of the Unique Local Address usage for private and
local addressing.
Appendix B. Revision historyB.1. Changes from *-vandevelde-v6ops-nap-00 to
*-vandevelde-v6ops-nap-01
o Document introduction has been revised and overview table added
o Comments and suggestions from nap-00 draft have been included.
o Initial section of -00 draft 2.6 and 4.6 have been aggregated into
a new case study section 5.
o The list of additional IPv6 benefits has been placed into
appendix.
o new security considerations section added.
o GAP analysis revised.
o Section 2.6 and 4.6 have been included.
B.2. Changes from *-vandevelde-v6ops-nap-01 to *-ietf-v6ops-nap-00
o Change of Draft name from *-vandevelde-v6ops-nap-01.txt to *-
ietf-v6ops-nap-00.txt.
o Editorial changes.
B.3. Changes from *-ietf-v6ops-nap-00 to *-ietf-v6ops-nap-01
o Added text in Chapter 2.2 and 4.2 to address more details on
firewall and proxy
o Revised Eric Klein contact details
o Added note in 4.2 that control over the proposed statefull-filter
should be by a simple user-interface
B.4. Changes from *-ietf-v6ops-nap-01 to *-ietf-v6ops-nap-02
o General Note: Header more consistent capitalized.
o Section 1: para 3: s/...and privacy and will... translation./
...and privacy. NAP will achieve these security goals without
address translation whilst maintaining any-to-any connectivity./
o Section 1: Various editorial changes happened
o Section 2.1: Changed: 'Frequently a simple user interface is
sufficient for configuring'. into 'Frequently a simple user
interface, or no user interface is sufficient'
o Section 2.2: (Simple Security ) Better not to use the word -evil-
in the text
o Section 2.2: changed 'provided by NAT are actually ' into
'provided by NAT is actually'
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o Section 2.2: para 3: s/actually false/actually an illusion/
o Section 2.2: para 2: added 'Also it will only be reliable if a
mechanism such as 'trusted computing' is implemented in the end-
system; without this enhancement administrators will be unwilling
to trust the behavior of end-systems.
o Section 2.3: para 1: s/of the NAT devices state/from the NAT
device's state/
o Section 2.4: para1: clarified the definition of topology hiding
o Section 2.4: last sentence of next-to-last paragraph, added
punctuation at end of sentence.
o Section 2.4: added first line: When mentioning 'topology hiding'
the goal is to make a reference that an entity outside the network
can not make a correlation between the location of a device and
the address of a device on the local network.
o Section 2.4: para 1: s/reflected/represented/
o Section 2.5: last par: added reference: 'Section 2.7 describes
some disadvantages that appear if independent networks using
[RFC1918] addresses have to be merged.'
o Section 2.6: Added text that private address-space is not
limitless
o Section 2.6: Various editorial changes
o Section 2.7: Para 1 editorial revised
o Section 2.7: last para: s/This solution/The addition of an extra
NAT as a solution/
o Section 2.7: s/highly desirable to be/highly desirable due to
resiliency and load-balancing to be/
o Section 2.7: added text on the reason why there are overlapping
addresses
o Section 2.7: last para: s/merged address space/overlapping address
spaces in the merged networks/
o Section 3.1: Para 1 editorial changes
o Section 3.1: s/by contacted web sites, so IPv6/by web sites that
are accessed from the device: IPv6 /
o Section 3.1: s/as that would have a serious negative impact on
global routing/as that would have a negative effect on global
route aggregation
o Section 3.2: s3.2: Par 1 editorial revised and noted that ULA in
global routing table is not scalable
o Section 3.2: s3.2: Noted that it is not always interesting to mix
ULA with global as that may lead to SAS issues
o Section 3.3: last para: s/delegating router/delegating router
(incorporating a DHCPv6 server)/, s/across an administrative/
possibly across an administrative/
o Section 3.4: Changed: 'random assignment has as purpose' to
'random assignment has a purpose'
o Section 3.4: para 2: Replace first sentence with: 'The random
assignment is intended to mislead the outside world about the
structure of the local network.'
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o Section 3.4: para 2: s/there is a correlation/needs to maintain a
correlation/
o Section 3.4: para 2: s/like a/such as a/
o Section 3.4: para 3: s/unpredictable/amorphous/, s/or from
mapping/and from mapping of/
o Section 3.4: para 3: s/are reachable on/are allocated to devices
on/
o Section 3.4: para 3: s/belonging to the same subnet next to each
other/belonging to devices adjacent to each other on the same
subnet/
o Section 3.4: s/aggregation device/indirection device/
o Section 4.1: split the 1 section up into 2 separate sections
o Section 4.1: s/ End node connections involving other nodes on the
global Internet will always use the global IPv6 addresses [9]
derived from this prefix delegation./ End node connections
involving other nodes on the global Internet will always use the
global IPv6 addresses [9] derived from this prefix delegation. It
should be noted that the policy table needs to be correctly set up
so that true global prefixes are distinguished from ULAs and will
be used for the source address in preference when the destination
is not a ULA/
o Section 4.1: A more secure network environment can be established
by having the referenced ULA addresses statically configured on
the network devices as this decreases the dynamic aspects of the
network, however the operational overhead is increased.
o Section 4.2: Added note that IID should be randomized for port-
scan protection
o Section 4.2: Removed text: This is an automated procedure of
sending Internet Control Message Protocol (ICMP) echo requests
(also known as PINGs) to a range of IP addresses and recording
replies. This can enable an attacker to map the network.
o Section 4.2: paragraph beginning: "This simple rule...". The
first sentence in this paragraph was overly-long. The sentence
has been fragmented
o Section 4.2: para 1: s/similar as for an/similar to that of an/
o Section 4.2: para 1: s/Internet, and firewall and IDS systems are/
Internet. The use of firewall and Intrusion Detection Systems
(IDS) is/
o Section 4.2: para 1: s/but has/but with/
o Section 4.2: para 1: s/end to end/end-to-end/
o Section 4.2: Item 3: s/amount/number/
o Section 4.2: Item 3: s/This goes from the assumption that the
attacker has no/This protection is nullified if the attacker has/
o Section 4.2: para after Item 3: s/pose/offer/ (or provide).
o Section 4.2: para after Item 3: s/best- practices/best practices/
o Section 4.2: para after example firewall rules: s/create similar
protection and security holes the typical IPv4 NAT device will
offer/provide (non-)protection and create security holes similar
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to those offered to a network using a typical IPv4 NAT device/
o Section 4.2: para next but one after firewall rules: s/What one
does when topology probing is to get an idea of the available
hosts/The intention of topology probing is to identify a selection
of the available hosts/
o Section 4.2: s/This is directly the opposite of what IPv6 security
best practices are trying to achieve./IPv6 security best practices
will avoid this kind of illusory security but can only do this if
correctly configured firewalls and IDS systems are used at the
perimeter where some IPv4 networks have relied on NATs.
o Section 4.2: s/ It is recommended for site administrators to take
[17] into consideration to achieve the expected goal./ It is
recommended for site administrators to take [17] into
consideration to achieve the expected goal. This protection will
also be nullified if IIDs are configured in a group near the start
of the IID space./
o Section 4.2: Removed the example study and added complementary
text to describe a potential behavior
o Section 4.4: rewrite of the section to reduce the importance of
the MIPv6 and tunneled solution
o Section 4.4: (Privacy and Topology Hiding) Mobile IP is suggested
in the text, however text is added that any kind of tunneling
should do the trick.
o Section 4.4: para 2: after 'As discussed above' inserted '(see
Section 3.1)'
o Section 4.4: para 3: s/consolidated on/indirected via/
o Section 4.4: para 3: s/topololgy masked/each topology masked/
o Section 4.4: para 3: Expanded acronym COA
o Section 4.4: para 3: s/rack mounted/static/
o Section 4.4: Rephrasing of text happened in this section
o Section 4.5: change: "so that a NAT is not required" to: "so that
IPv6 address translation is not required".
o Section 4.5: changed 'periodically to look' into 'to look
periodically'
o Section 4.5: change: "2^64 hosts" to: "2^64 addresses".
o Section 4.5: Removed the statement '(or even defined)
o Section 4.6: last para: s/which will lead to the IPv4 practice/
which will require the adoption of the IPv4 workaround/
o Section 4.6: s/the IPv4 constricting scenarios of multiple devices
sharing a/the constriction of IPv4 scenarios where multiple
devices are forced to share a/
o Section 4.7: s/as the zero-touch external/as an almost zero-touch
external/
o Section 5: Replaced first three sentences with: In presenting
these case studies we have chosen to consider categories of
network divided first according to their function either as
carrier/ISP networks or end user (such as enterprise) networks
with the latter category broken down according to the number of
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